Circuit means



CIRCUIT BRIGHTNESS CONTROL 35 T NT A a TE ka uo cs T E. rz-

T EL Ez z I IE I q 5 Y BY PMMJYEWO 13 ATTORNEYS INDICATING PANEL 3,061,828 CRCUIT MEANS Aloysius J. Hauck, Milwaukee, Wis., assignor, by mesne assignments, to Basic Products Corporation, Milwaukee, Wis a corporation of Wisconsin Filed Mar. 11, 1958, Ser. No. 720,776 Claims. (Cl. 340251) This invention relates to a system for detecting changes in a load circuit and especially one for indicating failure of lamps in a lighting system.

Airport runway lights normally are at some distance from the control tower so that it is difiicult to ascertain when any predetermined number have failed or burned out. Normally, the lamps in such an arrangement are fed from isolating transformers which are connected in series and it is desirable to be able to have an indication or warning at a remote point.

One of the objects of the invention is to provide a system which will detect and indicate failure of lamps in a lighting system.

Another of the objects of the invention is to provide an arrangement which will indicate at a remote location the condition or failure of parts of a lighting or similar system.

In one aspect of the invention, the detection means is arranged to respond to a change in a normally resistive load, such as is the case when a plurality of isolating transformers are connected in series, the secondaries of the transformers being connected to the lamps. When a lamp to which such a transformer is connected fails, the transformer primarily consumes load current as magnetizing current. The primaries of the isolating transformers may be fed from a constant current source of the resonant type, saturable type or high reactance type. Circuit means can be employed to provide a first signal, such as a voltage signal. The first signal can be obtained from a winding on an output transformer, if used, which feeds the load, or from a potential transformer connected across the load. The voltage of this signal will be in phase with the voltage across the series loop and proportional to the impedance of said loop. A second circuit means is provided for producing a second signal, such as voltage, displaced substantially 90 degrees from the load current. This signal can be obtained, for example, from a current transformer in the load circuit and an inductance in the secondary circuit of the current transformer. A combining circuit is employed combining the first and second signals or voltages in such a manner that when the load is normally resistive, or less than a predetermined number of lamps are out, the second signal plus one half of the first signal will be balanced by the second signal minus one half of the first signal. Then, if one of the lamps burns out, the load current and first signal will no longer be in phase because of the reactive impedance of the isolating transformer of the failed lamp and the combined signals will no longer be equal. A detecting means is provided to indicate a departure of the equal normal signal conditions as a result of a lamp burn out or to operate a relay for transmitting or using such departure information to a remote point.

These and other objects, advantages and features of the invention will become apparent from following description and drawings which are merely exemplary.

In the drawings:

FIG. 1 is a circuit diagram.

FIG. 2 is a showing of voltage relations when all lamps are burning.

FIG. 3 is similar to FIG. 2 but depicts voltage relation upon failure of lamp.

The invention will be described in conjunction with a lighting system but can be used in other similar ways.

3,061,828 Patented Oct. 30, 1962 Output transformer 10 may have its primary 11 connected to a constant current source of alternating current, such as a resonant type, saturable type, or high reactance type. The output transformer secondary 12 is connected to a load circuit including a plurality of isolating transformers 13 having their primaries connected in series with secondary 12. The secondaries of isolating transformers 13 are connected in the usual manner to lamps 14.

Output transformer 10 may have a center-tapped winding 15 for providing a voltage or signal which will be in phase with the voltage across the series load loop and proportional to the impedance of said loop. As an alternative, the voltage or first signal also'could be obtained by connecting a potential transformer across the series loop if it is desired to omit output transformer 10. Current transformer 16 may have its primary connected in series with the series load circuit. Ammeter or indicator 17 can be connected to the secondary circuit of the current transformer through winding 18 of mutual inductance 19. Resistance 20 also may be included but may be omitted if an exact quadrature relationship is not required.

Combining resistance 21 can be considered to be composed of two parts 22, 23. Resistance 22 can have one side connected to Winding 15 through line 24 and rectifier 25. Resistance 23 may have one side connected to winding 15 through line 26 and rectifier 27. Center tap 28 of winding 15 is connected to center tap 29 of resistance 21 through mutual inductance 19 or similar means.

Under normal operating conditions with all of the isolating transformers loaded, current in the load circuit and voltage induced in winding 15' will be substantially in phase. Under this condition, the voltage E plus and E minus netizing current is reactive. When this occurs, the condition 1 E3 plus 2 and E minus will become unequal in magnitude as illustrated in FIG. 3 and Will cause a net direct current voltage to appear across resistor 22 plus resistor 23. The magnitude of said voltage will be proportioned to the number of lamps that have failed.

Inasmuch as said direct current voltage will have a.

high ripple, it is desirable to use a filter including inductance 30 and capacitance 31 in the circuit feeding the sensitive relay or meter 32.

There can be an adjustable resistor 33 included in the indicating circuit so as to cause or permit adjustment of meter contacts closure for various percentages of burned out lamps. If the voltage E across winding 15 is made several times as large as voltage E across inductance 19, the need for close adjustment of resistor I 33 will be eliminated. Relay 32 may be connected, if

. desired, to an indicating panel 34 remotely located relative thereto such as in "a control tower to operate a warning light or signal.

It has been found that the system is very sensitive and will detect satisfactorily failure of one light out of a hundred. As an example, the meter readings for varying percentages of open isolating transformers relative to full load were found to be:

Percent: D.C. meter reading .200 2% .500 4 /2 .600 6% .700 9 .800 11 .4 s .900

The arrangement also can be used in, conjunction with a brightness control circuit indicated schematically at 35 such as illustrated in copending application Serial No. 720,777, filed March 11, 1958.

' It should be apparent that variations can be made in details of the circuit and use thereof for detecting change in inductance in a load circuit without departing from the invention except as defined in the appended claims.

that during a normal condition when all of the lamps are burning, said second voltage plus one-half of said first voltage will be equal to said second voltage minus one half of said first voltage, the combined voltage :for said normal condition having no direct net value, and means indicating a departure of said combined voltage of said combining means from said normal condition be cause of lamp failure.

2. In a detection means for determining failure of lamps in a normally resistive load, said lamps being connected to series connected isolating transformers, the combination including means for producing a first voltage in phase with the load voltage, current transformer means connected in series with the series connected isolating transformers, reactive means connected to said current transformer means for producing a second voltage displaced substantially 90 from the load current, combining circuit means connected to said means for producing a first voltage and to said reactive means for producing said second voltage to combine said first and second voltages so that during a normal condition when said lamps are burning, said second voltage plus one-half of said first voltage will be equalto said second voltage minus one-half of said first voltage, the combined voltage for said normal condition having no direct net value, and condition responsive means responsive to a departure of said combined voltage of said combining circuit means from said normal condition because of failure of lamps in said load.

3. In a detection means for determining failure of lamps in a normally resistive load, said lamps being connected to series connected isolating transformers, the combination including means for producing a first voltage in phase with the load voltage, current transformer means connected in series with the series connected isolating transformers, reactive means connected to said current transformer means for producing a second voltage dis placed substantially from the load current, combining circuit means connected to said means for producing a first voltage and to said reactive means for producing said second voltage to combine said first and second voltages so that during a normal condition when said lamps are burning, said second voltage plus one-half of said first voltage will be equal to said second voltage minus onehalf of said first voltage, the combined voltage for said normal condition having no direct net value, filter circuit means connected to said combining circuit means, and condition responsive means connected to said filter circuit means, said condition responsive means being responsive to a departure of said combined voltage of said combining means from said normal condition as said filter circuit means when failure of lamps in said load occurs.

4. In a system for determining failure of lamps, the combination including a constant current source, a plurality of isolating transformers connected in series with said source to provide a load circuit, means for connecting lamps to said isolating transformers, a first voltage producing means connected to said sources for producing a first voltage in phase with the load voltage, a current transformer connected in said load circuit, circuit means connected to said current transformer for producing a voltage displaced substantially 90 from the load current, combining circuit means connected to said first voltage producing means and to said circuit means connected to said current transformer to combine said first voltage and said voltage displaced substantially 90 from the load current, said combining circuit means producing a resultant voltage upon predetermined changes of load circuit conditions, and resultant voltage responsive means connected to said combining circuit.

5. In a system for determining failure of lamps the combination including a constant current source, an output transformer, a plurality of isolating transformers connected in series with said source to provide a load circuit, means for connecting lamps to said isolating transformers, a first voltage producing means connected with said output transformer for producing a first voltage in phase with the load voltage, a current transformer connected in said load circuit, circuit means connected to said current transformer for producing a voltage displaced substantially 90" from the load current, combining cir-cuit means connected to said first voltage producing means and to said circuit means connected to said current transformer to combine said first voltage and said voltage displaced substantially 90 from the load current, said combining circuit means including a pair of resistance means and rectifiers for producing a resultant D.C. signal upon predetermined changes of load circuit conditions, and resultant signal responsive means connected to said combining circuit.

References Cited in the file of this patent UNITED STATES PATENTS 2,424,131 Warnick July 15, 1947 2,431,794 Dichter Dec. 2, 1947 2,449,739 Duttera Sept. 21, 1948 2,474,290 Terry ct al June 28, 1949 2,794,928 Frank June 4, 1957 2,817,076 Graves Dec. 17, l957 FOREIGN PATENTS 550,135 Great Britain Dec. 24, 1942 

